Sulfur aromatic compounds in crude oils from Egypt

ABSTRACT

Sulfur is usually the most abundant hetero element in petroleum and is also common in other types of fossil organic matter[1] Most of the sulfur present in crude oils, bitumens and kerogens is organically-bound sulfur, i.e. bound to carbon; hydrogen sulphide and elemental sulfur dissolved in crude oils usually are a very minor portion of the total sulfur[2]- Organically-bound sulfur in crude oils is mainly present in medium [as single compounds] and heavy fractions [as part of complex molecules; i.e. asphaltenes and resins]. Sulfur compounds have been and are of interest to the petroleum industry for four major reasons. [1] 1] Organic sulfur compounds [OSC] can cause problems during processing of petroleum i.e. they poison catalysts and cause corrosion to metal vessels and pipelines; 2] they impart undesirable characteristics to the products derived from the crude oils; 3] sulfur dioxide is produced during combustion of sulfur-containing fuels, which causes global environmental problems, .e.g. acid rain problem; and 4] its geochemical significance i.e. in providing information on the origin and composition and the geochemical and geological history of petroleum. [3] To solve, systematically, the problem of removing the sulfur compounds from petroleum or its products, or to render these compounds harmless, a knowledge of the type, structure, and chemical nature of the compounds present is desirable. Therefore, a systematic characterization of the sulfur compounds in crude oils has both theoretical and practical value. The identification of OSC started in the nineteenth century with the identification of ten alkyl sulfides in Ohio crude oil [4] and thiophene in Gromy crude oil. [5]Ever since, the number and structural complexity of OSC identified has increased significantly, as comprehensively reviewed by Gal'pern, [6-8] Orr, [2] Thompson, [9] Aksenov and Kamayanov,[10] Orr and Sinninghe Damste [11] and Sinninghe Damste and de Leeuw[3] Thiophene derivatives [benzothiophenes, dibenzothiophenes, and naphthbenzothiophenes] are known to be one of the most important petroleum sulfur compound types, constituting 45-84 percent of sulfur compounds in middle and high boiling fractions[10] In previous work[12], the distribution of paraffins, triterpenoidal alkanes and aromatic hydrocarbons in Alamein and Badran crude oil samples from Egypt have been studied. The results indicated that the oils were sourced from type II/III kerogens with preponderant terrestrial components. Further, the triterpane maturityindicator based on the ratio of the two trisnorhopanes [T[s] / T[m]] showed that alamein oil has a more advanced level of thermal maturity. In continuation of the study, the present paper reports on the occurrence and distribution of thiophenic compounds in the same oil samples. An evaluation of the distribution patterns of these compounds as maturity indicators is also presented